Enforce the use of === and !==

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Metadata

ID: javascript-code-style/strict-equals

Language: JavaScript

Severity: Notice

Category: Best Practices

Description

In JavaScript, == and != comparisons do type coercion, which can be confusing and may introduce potential errors. Use the type-safe equality operators === and !== instead.

Non-Compliant Code Examples

b == c

foobarbaz == true
foobar != 1
plop == undefined

a == b;
a != b;
typeof a == 'number';
typeof a == 'number';
'string' != typeof a;
2 == 3;
2 == 3;
'hello' != 'world';
'hello' != 'world';
a == null;
a == null;
null != a;
true == 1;
0 != '1';
'wee' == /wee/;
typeof a == 'number';
'string' != typeof a;
'hello' != 'world';
2 == 3;
true == true;
true == null;
true != null;
null == null;
null != null;
a
==
b;
(a) == b;
(a) != b;
a == (b);
a != (b);
(a) == (b);
(a == b) == (c);
(a != b) != (c);
a == b;
a!=b;
(a + b) == c;
(a + b)  !=  c;
((1) )  ==  (2);

Compliant Code Examples

'foo' != 'bar'
51 == 42
true == true
foobarbaz == null
typeof foo == 'undefined'

a === b
a !== b
a === b
a !== null
a === null
a !== null
null === null
null !== null

// https://github.com/eslint/eslint/issues/8020
foo === /abc/u

// bigint
foo === 1n
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